1. Field of the Invention
The present invention relates generally to manufacture and use of wafer level optics with optical heads and more particularly to manufacture and use of a high numerical aperture (NA) objective micro-lens through an assembly of subcomponents that can be produced in an array format using wafer-level techniques.
2. Background Art
Prior to this invention, the manufacture of high numerical aperture objective lens involved a molding and a polishing of an aspheric surface using a high-index (of refraction) glass, techniques not capable of producing micro-lenses at high production rates. Current methods of producing a micro-part makes use of wafer-level processes, which can include an etch (ion milling), or a photoresist reflow technique. However, these processes are generally limited to a low-index glass (typically silica) with a spherical or near-spherical surface, or to a diffractive surface, preventing their use in the fabrication of high-quality, high numerical aperture lens.
Information storage technology and the storage capacity available therefrom has historically been limited by a number of factors. A typical prior art Winchester magnetic storage system includes a magnetic head that has a body and a magnetic read/write element and is coupled to a rotary actuator magnet and coil assembly by a suspension and actuator arm so as to be positioned over a surface of a spinning magnetic disk. In operation, lift forces are generated by aerodynamic interactions between the magnetic head and the spinning magnetic disk. The lift forces are opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk.
Head designs are being used with other storage technologies, in particular, magneto-optical (MO) storage technology. In one type of MO storage system, a magneto-optical head assembly is located on an actuator that moves the head along a radial direction of the disk to position the optical head assembly over data tracks during recording and readout. A magnetic coil is placed on a separate assembly on the head assembly to create a magnetic field that has a magnetic component in a direction perpendicular to the disk surface. A vertical magnetization of polarity, opposite to the surrounding material of the medium, is recorded as a mark indicating zero or a one by first focusing a beam of laser light to form an optical spot on the disk. The optical spot functions to heat the magneto-optical material to a temperature near or above a Curie point (i.e. a temperature at which the magnetization may be readily altered with an applied magnetic field). A current, passed through the magnetic coil, orients the spontaneous magnetization either up or down. This orientation process occurs only in the region of the optical spot where the temperature is suitably high. The orientation of the magnetization mark is preserved after the laser beam is removed. The mark is erased or overwritten if it is locally reheated to the Curie point by the laser beam while the magnetic coil creates a magnetic field in the opposite direction.
Information is read back from a particular mark on the disk by taking advantage of the magnetic Kerr effect to detect a Kerr rotation of the optical polarization that is imposed on a reflected light beam by the magnetization at the mark of interest, the magnitude of the Kerr rotation being determined by the material's properties (embodied in the Kerr coefficient). The sense of the rotation is measured by established differential detection schemes as being clockwise or counter-clockwise depending on the direction of the spontaneous magnetization at the mark of interest.
Conventional magneto-optical heads tend to be based on relatively large optical assemblies which make the physical size of the head rather bulky. Consequently, the speed at which conventional MO heads are mechanically moved to access new data tracks on a MO storage disk, known as a `seek time` is slow. In addition, due to the large size of these optical assemblies, most commercially available MO disk drives use only one MO head to enable reads and writes to one side of a MO disk at a time.
Magneto-optical information access requires the use of polarized laser light for reading and writing information on an MO disk. In the case of reading information, MO technology makes use of the magneto-optical effect ("Kerr" effect) to detect a modulation of polarization rotation imposed on the linearly polarized incident laser beam by the recorded domain marks in the recording layer. The polarization rotation (representing the information stored at recorded marks or in the edges of the recorded marks) is embodied in a reflection of the linearly polarized laser beam and is converted by optics and electronics for readout. Magneto-optical technology allows for increased storage capacity with drives through the ability to store information on the particular storage disk with an increased areal density.
Larger capacity MO drives can be designed by increasing the number of disk platters and attendant read/write MO heads (over the current MO convention); this requires the provision of a MO head for each side of each disk platter. In these designs an increase in the rate of information transfer from the hard drive is desirable. The factors which effect overall information transfer from a hard drive include: a data-transfer rate, the head `seek` time (a function of a rate of movement of the actuator-arm-head assembly), and a drive rotation rate. Therefore, as the areal density increases, and the number of MO heads per drive increases, it is a corollary that the MO head size will need to be decreased for packaging reasons as well as to improve performance.
To this end and others, what is needed is a method for manufacturing micro-lenses, alone or in combination with an optical head, with high numerical aperture, and/or by using the large volume processes of wafer production.